Replacement apparatus for an optical element

ABSTRACT

A replacement apparatus for an optical element mounted between two adjacent optical elements in a lithography objective has a holder for the optical element to be replaced, which holder can be moved into the lithography objective through a lateral opening in a housing of the same.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a replacement apparatus for an optical elementarranged between two adjacent optical elements in a lithographyobjective. Furthermore, the invention relates to a lithographyobjective.

2. Description of the Prior Art

Lithography objectives are known in which the last optical element, thatis to say the one located closest to the wafer to be exposed, isreplaceable.

Furthermore, projection objectives exist in which lens barrels are heldin a support structure and can be replaced in their entirety. In orderto make this possible, it is necessary to break down the entirestructure of the objective.

With regard to the prior art relating to the invention, reference ismade to the documents U.S. 2002/0167740 A1 and U.S. Pat. No. 6,449,106B1.

If the optical elements within a lithography objective, such as lensesor mirrors, for example, change over the course of time and impair theperformance of the objective in such a way that the intended lifetime ofthe same cannot be achieved, it should be possible to remove anappropriately selected optical element within the objective and, forthis, to insert a new, appropriately machined optical element, whichcompensates for the imaging errors of the other optical elements. Theknown procedures and apparatus for replacing the last optical elementare not suitable for this purpose, however.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide areplacement apparatus for an optical element mounted between twoadjacent optical elements in a lithography objective, which permits sucha replacement.

According to the invention, for this purpose, a replacement apparatus isprovided for an optical element mounted between two adjacent opticalelements in a lithography objective, having a holder for the opticalelement to be replaced, which holder can be moved into the lithographyobjective through a lateral opening in a housing of the same.

This replacement apparatus is capable of removing the optical elementfrom the lithography objective and of moving another optical element,matched specifically to the changes within the lithography objective,into the lithography objective again. By these means, the imagingperformance of the lithography objective can be improved considerablywithout any intervention in the structure of the lithography objective.All that is necessary is a lateral opening in the housing of thelithography objective, which is dimensioned such that the holder canmove into the housing. In this case, the holder is capable ofpositioning the optical element very accurately within the lithographyobjective.

The replacement apparatus according to the invention may be usedparticularly advantageously in a lithography objective comprising aplurality of optical elements. Suitable for this purpose is alithography objective having a plurality of optical elements, at leastone replacement apparatus for an optical element mounted between twoadjacent optical elements, and having a holder for the optical elementto be replaced, which holder can be moved into the lithography objectivethrough a lateral opening in a housing of the same.

Various exemplary embodiments of the invention are illustrated inprinciple below by using the drawing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a lithography objective having a plurality of opticalelements and a replacement apparatus;

FIG. 2 shows a section along the line II-II from FIG. 1 with a firstembodiment of the replacement apparatus;

FIG. 3 shows the optical element with a stiffening element;

FIG. 4 shows a second embodiment of the replacement apparatus;

FIG. 5 shows a third embodiment of the replacement apparatus;

FIG. 6 shows a schematic representation of the mounting of the opticalelement;

FIG. 7 shows a first embodiment of a seal for the opening in the housingof the lithography objective;

FIG. 8 shows a second embodiment of a seal for the opening in thehousing of the lithography objective;

FIG. 9 shows a fourth embodiment of the replacement apparatus; and

FIG. 10 shows a view in accordance with the arrow X from FIG. 9.

DETAILED DESCRIPTION

FIG. 1 shows lithography objective 1 with a housing 1 a, in which, in amanner known per se, a plurality of optical elements 2, such as lenses,plates or mirrors for example, are arranged. The arrangement of theoptical elements 2 within the lithography objective 1 should in thiscase be seen as purely exemplary. The lithography objective 1 can besuitable for any type of lithography and can be part of an exposureapparatus not shown in its entirety in the drawings. Using thelithography objective 1 illustrated, it is possible, as described below,to replace an optical element 2 a which is mounted or held between twoadjacent optical elements 2 preferably installed permanently in thelithography objective 1 by means of respective mounts 3 and thus notreplaceable. The replaceable optical element 2 a, which is preferablylikewise a lens, a plate or a mirror, can be seen in the sectionalillustration according to FIG. 2 and is preferably located in a pupilregion of the lithography objective 1. As a result, the replaceableoptical element 2 a can be designed with a particularly small diameteras compared with the other optical elements 2. However, the replaceableoptical element 2 a can be located at any other point between twoadjacent optical elements 2 installed in the lithography objective 1.

In order to replace the optical element 2 a, a replacement apparatus 4is provided, which can likewise be seen better in FIG. 2. Thereplacement apparatus 4 has a holder 5 for the optical element 2 a,which can be moved into the lithography objective 1 through a lateralopening 6 in the housing 1 a of the lithography objective 1. In thepresent embodiment, illustrated very simplified, the opening 6 is formedby a plurality of spacer elements 7 on the periphery of the housing 1 a.If, as described above, the replaceable optical element 2 a is locatedin the pupil region of the lithography objective 1, this permits acorrespondingly small size of the holder 5 and, accordingly, also of theopening 6. It is to be preferred if the spacer elements 7 are arrangedsymmetrically, in order not to impair the dynamic behavior of thelithography objective 1 in an impermissible way. The maximum diameter ofan optical element 2 a to be replaced is given by three spacer elements7.

In order to replace or change the optical element 2 a, the holder 5moves through the opening 6 into the lithography objective 1 and removesthe optical element 2 a to be replaced. After the holder 5 has left thelithography objective 1 through the opening 6 again, the optical element2 a can be removed from the holder 5 outside the lithography objective1. Then, with the aid of tools, not illustrated, outside the lithographyobjective 1, a new optical element 2 a is inserted into the holder 5 andthe holder 5 moves through the opening 6 into the housing 1 a of thelithography objective 1. The movement of the holder 5 is in each caseindicated by the arrow designated “A”.

The newly introduced optical element 2 a has previously been machinedexactly to the requirements within the lithography objective 1 and iscapable of compensating for imaging errors which have resulted over thetime of use of the lithography objective 1. The measures taken on theoptical element 2 a for this purpose can be intrinsically known andshould therefore not be part of the present application. Following thepositioning of the optical element 2 a within the lithography objective1, the holder 5 leaves the lithography objective 1 again through theopening 6.

FIG. 3 shows the replaceable optical element 2 a, which is connected toa stiffening element 8. The stiffening element 8, which is ring-like inthe embodiment illustrated, preferably consists of substantially thesame optical material as the replaceable optical element 2 a, of SiO₂ inthe present case, and is used to stiffen the optical element 2 a, inparticular during the transport of the same. The stiffening element 8 isparticularly expedient in the case of flexible optical elements 2 a. Ofcourse, the optical element 2 a can also consist of CaF₂ or anothersuitable optical material.

The connection of the stiffening element 8 to the replaceable opticalelement 2 a can be made by wringing, by adhesive bonding, by solderingor in another suitable manner. If the stiffening element 8 does notconsist of the same optical material as the optical element 2, then itshould preferably have an approximately identical coefficient of thermalexpansion to the optical element 2 a. If this is not the case either,then a connection between the stiffening element 8 and the opticalelement 2 a via solid-body linkages, not illustrated, can be provided.Furthermore, it is also possible to hold the optical element 2 a in itsown mount.

From FIG. 3, it is further possible to see that the holder 5 acts bothon the optical element 2 a and on the stiffening element 8. Of course,the holder 5 can also act only on the stiffening element 8.

A second embodiment of the replacement apparatus 4 is illustrated inFIG. 4. Once again, the replaceable optical element 2 a is arrangedbetween two optical elements 2 mounted in the lithography objective 1 bymeans of respective mounts 3. In order to hold and to mount the opticalelement 2 a within the lithography objective 1, use is made of aseparate holding structure 9 which, in this case, is placed on mount 3of the adjacent optical element 2 a, which is located underneath thereplaceable optical element 2 a. Although this is not illustrated, theoptical element 2 a could also be provided with the stiffening element 8in this case. The separate holding structure 9 preferably has threesupports 10, of which only two can be seen in the illustration accordingto FIG. 4. To this extent, this is an isostatic mounting of the opticalelement 2 a within the lithography objective 1. In addition, theseparate holding structure 9 has a plurality of actuators 11, which arecapable of aligning the optical element 2 a in particular in thez-direction, that is to say in the direction of the optical axis of thelithography objective 1, tilting of the optical element 2 a also beingpossible. In the present case, each support 10 is assigned to one of theactuators 11. Of course, only one actuator 11 could also be providedand, furthermore, it would be possible to accommodate respectivemanipulators in the holding structure 9 instead of the actuators 11.

In order to hold and to mount the optical element 2 a in a definedmanner within the lithography objective 1 following its replacement andto secure the same, a plurality of spring elements 12 are providedwhich, in the present case, are supported on the mount 3 of the opticalelement 2 arranged above the replaceable optical element 2 a. The springelements 12 can be controllable by means of devices, not illustrated, inorder, following the deposition of the optical element 2 a on theholding structure 9, to press the same against the holding structure 9and, in this way, to ensure accurate positioning of the optical element2 a in the z-direction, that is to say in the direction of the opticalaxis of the lithography objective 1. If appropriate, only one springelement 12 acting on the optical element 2 a could also be provided. Inorder to deposit the optical element 2 a on the holding structure 9, amovement of the holder 5 in the z-direction can be necessary. Thus, theholding structure 9, like the aforementioned mount as well, is used tomount the optical element 2 a in the lithography objective 1 during theuse of the same.

FIG. 4 further reveals that the opening 6 in the housing 1 a can beclosed by a seal 13. In the embodiment according to FIG. 4, this is asolid material seal or gasket, various embodiments of the seal 13 beingexplained later. The seal 13 preferably remains in place during theoperation of the lithography objective 1 and is removed only in order tomake the opening 6 accessible to the holder 5 in order to replace theoptical element 2 a.

In the embodiment of the replacement apparatus 4 according to FIG. 5,the replaceable optical element 2 a is again provided with thestiffening element 8. In a way similar to that in the embodimentaccording to FIG. 4, the holding structure 9 is also provided here, andis again supported on the mount 3 of that optical element 2 which islocated underneath the replaceable optical element 2 a. Instead of thesupports 10, the holding structure 9 is in this case provided with amount 14 which rests on the mount 3. Of course, the spring elements 12or the at least one spring element 12 could act on the optical element 2a in this embodiment as well.

In an embodiment which is not illustrated, the replaceable opticalelement 2 a could also rest directly on the mount 3 of the opticalelement 2 located underneath. In this case, attracting the opticalelement 2 a by means of vacuum, and therefore corresponding fixing, ispossible.

FIG. 6 shows an illustration of the principle of one possible way ofmounting the optical element 2 a within the housing 1 a of thelithography objective 1. The optical element 2 a is again provided withthe stiffening element 8 and, via the stiffening element 8, is mountedwith respect to the housing 1 a by means of a loose bearing 15 and afixed bearing 16 with the effect of an isostatic mounting. Both theloose bearing 15 and the fixed bearing 16 can consist of hard metal, ofhardened steel or of a precious stone, for example of ruby.

A first embodiment of the seal 13 for sealing the opening 6 of thehousing 1 a is illustrated in FIG. 7. In this case, a cover plate 17 isprovided, which is sealed with respect to the housing 1 a via an O-ring18. In this way, contamination of the interior of the housing 1 a of thelithography objective 1 is prevented, at the same time the accessibilityof the opening 6 being ensured. Instead of the solid material seal, anelastic gasket or a metal seal or a Viton seal can also be used. If ametal seal is used, its material can for example be copper.

The embodiment of the seal 13 according to FIG. 8 is a gas seal or agas-dynamic restrictor, which is based on the principle that, by meansof the pressure p_(i) within the housing 1 a of the lithographyobjective 1, which is increased by comparison with the pressure p_(a)outside the housing 1 a, no gaseous substances or other contaminants canpenetrate into the housing 1 a. For this purpose, the cover plate 17 isagain provided to be fastened opposite the housing 1 a with a slit 19which has a width from about 1 to 10 μm. In order to preventcontaminating substances being able to get into the interior of thelithography objective 1, care must merely be taken that the pressurep_(i) in the interior of the housing 1 a is greater than the pressure paoutside the housing 1 a and, in this way, a directed flow takes placefrom the interior of the lithography objective 1 to the outside.

FIGS. 9 and 10 show a further embodiment of the replacement apparatus 4for replacing the optical element 2 a. In this case, the holder 5 of thereplacement apparatus 4 has a guide 20 in the form of two lateralgrooves 21, into which respective lateral protrusions 22 belonging tothe optical element 2 a engage. The lateral protrusions 22 are notabsolutely necessary, however. In the case of a planar plate, theoptical element 2 a can be guided with its edge in the grooves 21. Inthe present case, as can be seen in FIG. 10, the grooves 21 and theprotrusions 22 are rectangular, but could also have any other suitablecross section. The movement of the optical element 2 a into the holder 5is limited by a spring bearing 23 which, together with a fixed bearing24 on the open side of the holder 5, ensures exact positioning of theoptical element 2 a inside the holder 5. At the same time, the fixedbearing 24 serves as a closure for the holder 5. To this extent, thegrooves 21 serve only to guide the optical element 2 a during thereplacement, whereas the position of the optical element 2 a isdetermined by the spring bearing 23 and the fixed bearing 24. Of course,the fixed bearing 24 can be provided with a suitable seal similar to theseal 13 in order to close the opening 6 hen the holder 5 is locatedinside the lithography objective 1. Furthermore, a spring element 25 isprovided which, similarly to the spring elements 12 according to theembodiment of FIG. 4, ensures accurate positioning of the opticalelement 2 a in the z-direction.

In this embodiment, provision is made for the holder 5 to remain withinthe lithography objective 1 during the transport and during theoperation of the same and hence, in addition to the possibility ofreplacing the optical element 2 a, also forms a mount for the same. Ifappropriate, the holder 5 could also remain within the lithographyobjective 1 in the other embodiments, if measures suitable for thispurpose are taken.

The lithography objective 1 described above can be part of an exposureapparatus and is provided for manufacturing microstructured componentssuch as wafers.

1. Replacement apparatus for an optical element mounted between twoadjacent optical elements in a lithography objective, having a holderfor the optical element to be replaced, which holder can be moved intothe lithography objective through a lateral opening in a housing of thesame.
 2. Replacement apparatus according to claim 1, wherein the opticalelement to be replaced is arranged between two non-replaceable opticalelements.
 3. Replacement apparatus according to claim 1, wherein theoptical element is connected to a stiffening element.
 4. Replacementapparatus according to claim 3, wherein the stiffening elementsubstantially consists of the same optical material as the opticalelement.
 5. Replacement apparatus according to claim 3, wherein thestiffening element is connected to the optical element by wringing. 6.Replacement apparatus according to claim 3, wherein the stiffeningelement is connected to the optical element by adhesive bonding. 7.Replacement apparatus according to claim 1, wherein the optical elementis held in a mount.
 8. Replacement apparatus according to claim 1,wherein the optical element is mounted within the lithography objectiveby isostatic mounting.
 9. Replacement apparatus according to claim 1,wherein the optical element is deposited within the lithographyobjective on a mount of an adjacent optical element.
 10. Replacementapparatus according to claim 1, wherein the optical element is held on aseparate holding structure within the lithography objective. 11.Replacement apparatus according to claim 10, wherein the separateholding structure has at least one actuator.
 12. Replacement apparatusaccording to claim 10, wherein the holding structure is held in a mountwithin the lithography objective.
 13. Replacement apparatus according toclaim 1, wherein at least one spring element acting on the replaceableoptical element in the direction of the optical axis is arranged withinthe lithography objective.
 14. Replacement apparatus according to claim1, wherein the opening in the housing is closeable by a seal. 15.Replacement apparatus according to claim 14, wherein the seal is a solidmaterial seal or gasket.
 16. Replacement apparatus according to claim14, wherein the seal is a gas seal.
 17. Replacement apparatus accordingto claim 1, wherein the holder has a guide for the replaceable opticalelement.
 18. Lithography objective having a plurality of opticalelements, at least one replacement apparatus for an optical elementmounted between two adjacent optical elements, and having a holder forthe optical element to be replaced, which holder can be moved into thelithography objective through a lateral opening in a housing of thesame.
 19. Lithography objective according to claim 18, wherein thereplacement apparatus is arranged in a pupil region of the lithographyobjective.
 20. Lithography objective according to claim 18, wherein theholder remains within the lithography objective following thereplacement of the optical element.
 21. Lithography objective accordingto claim 18, wherein the holder is removed from the lithographyobjective following the replacement of the optical element.
 22. Methodof manufacturing microstructured components by using a lithographyobjective according to claim 18.